Lawmakers will already be facing a time crunch when the Senate returns Monday.

The Centers for Medicare and Medicaid Services has been withholding payments to doctors treating Medicare patients to give Congress a window to work through a long-term resolution to the Sustainable Growth Rate problem that sees physicians regularly facing draconian cuts in payment rates without a patch known as a "doc fix."

The speaker's office has touted the deal as "Titanic Entitlement Reform" — complete with Leonardo DiCaprio GIFs — but some conservatives inside and outside the Capitol quibble with the idea the long-term bill will prove a better deal for taxpayers than the current system, citing a $141 billion price tag over 10 years.

Senate Majority Leader Mitch McConnell, R-Ky., says the "doc fix" is an immediate priority in his chamber, but just how quickly he can move it is an open question, given the veracity of opposition from some deficit hawks within the Republican Conference. That bloc of conservative senators may offer an amendment designed to require the bill be fully offset using traditional budget scoring rules.

Still, shortly before the break, one GOP lawmaker said he expected the Boehner-Pelosi bill would have overwhelming support in the Senate.

As the "doc fix" debate plays out on the floor, there will be no shortage of activity at the committee level. There are two big markups already on the Tuesday schedule — one on foreign policy and one on the domestic side.

At the Foreign Relations Committee, Chairman Bob Corker, R-Tenn., is set to call up his measure to give Congress a voice in the approval of a final agreement with Iran about that country's nuclear development. The Obama administration has publicly opposed the measure, arguing it could upend negotiations.

Democrats have already drafted a variety of amendments to the bill championed by Corker and Sen. Robert Menendez, D-N.J. Most notable in the early batch are proposals from Sens. Chris Coons of Delaware and Christopher S. Murphy of Connecticut that call for stripping certification requirements about the Iranian regime disavowing terrorism.

There's also expected to be no shortage of closed briefings and consultations with lawmakers about the framework agreement that was reached with Iran and announced during the recess.

National Security Council spokeswoman Bernadette Meehan told CQ Roll Call in an email that a variety of Cabinet members and other senior administration officials had been reaching out to members of Congress, in addition to calls to Corker and congressional leaders made by President Barack Obama.

The administration also planned what Meehan described as "detailed briefings to Members of Congress upon their return from recess."

"We will keep an open line of communication about all of the details of the agreement moving forward. And in the coming weeks, we'll engage Congress about how it can play a constructive oversight role," she said.

McConnell has already said the Senate would "respond legislatively" through Corker's legislation.

The same day Foreign Relations meets on Iran, the Health, Education, Labor and Pensions Committee is set to mark up legislation that represents an agreement between Chairman Lamar Alexander, R-Tenn., and ranking Democrat Patty Murray of Washington on a long-awaited successor to the elementary and secondary education law currently known as No Child Left Behind.

Alexander is a former member of the Republican leadership and an ally of McConnell, while Murray is the secretary of the Democrats, No. 4 in their leadership structure and an influential voice in leadership-level maneuvering. So if the HELP Committee successfully reports out a bill, it could actually find its way to the floor.

"While there is still work to be done, this agreement is a strong step in the right direction that helps students, educators, and schools, gives states and districts more flexibility while maintaining strong federal guardrails, and helps make sure all students get the opportunity to learn, no matter where they live, how they learn, or how much money their parents make," Murray said in a statement.